Thread cutter for sewing machine



y 7, 968 R. E. DAVY 3,381,644

THREAD CUTTER FOR SEWING MACHINE Filed Feb. 18, 1966 I 2 Sheets-Sheet 1 Hil l N VEN TOR. ROBERT E. DAVY 80 BY I; & t:

y 7, 1968 R. E. DAVY 3,381,644

THREAD CUTTER FOR SEWING MACHINE Filed Feb. 18, 1966 2 Sheets-Sheet 3 IN VEN TOR.

ROBERT E. DAVY BY mam United States Patent ()fice Patented May 7, 1968 3,381,644 THREAD CUTTER FOR SEWING MACHINE Robert E. Davy, La Mesa, Califl, assignor to Coroga Co., Anaheim, Calif. Filed Feb. 18, 1966, Ser. No. 528,487 6 Claims. (Cl. 112-252) ABSTRACT OF THE DISCLOSURE The thread cutter is adaptable to most sewing machines, particularly industrial types, and is operable by various means to cut the thread at the end of a line of stitching, the action of the cutter not being critical in relation to the needle stroke or timing of the mechanism. The simple The present invention relates to sewing machines and specifically to a thread cutter for a sewing machine.

In industrial type sewing machines which are used constantly, it is not practical to cut the thread manually at the end of each seam. This is especially true in the case of machines operating automatically or semi-automatically in an assembly operation, performing timed, interrupted stitching of successive seams. Thread cutters have been developed which are synchronized with the stitching mechanism to extend and cut the thread at the end of a seam, but these must be precisely timed and positioned to prevent interference with the needle and jamming of the mechanism.

The primary object of this invention, therefore, is to provide a thread cutter which does not require precise synchronization with the stitching mechanism and which will not interfere with the needle or mechanism in any way, even in the extended cutting position.

Another object of this invention is to provide a thread cutter which is held accurately in cutting position by a positive, readily adjustable stop and requires only a simple retracting and releasing mechanism for its operation.

Another object of this invention is to provide a thread cutter having a circular blade with an annular cutting edge, which is easily turned to advance a new section of edge at intervals and is readily removed when complete sharpening is necessary.

A further object of this invention is to provide a thread cutter which operates in such a manner that the cutting action automatically secures the last stitch of the seam against unravelling.

Another object of this invention is to provide a thread cutter which is adaptable to many types of existing machines and can be coupled to the machine mechanism in a variety of ways, or actuated by independent means if required.

The thread cutter and its installation in a typical machine are illustrated in the drawings, in which:

FIGURE 1 is a side elevation view of a sewing machine showing the position of the thread cutter;

FIGURE 2 is an enlarged sectional view taken on line 2-2 of FIGURE 1;

FIGURE 3 is a further enlarged view taken in the direction of arrows 3-3 in FIGURE 2;

FIGURE 4 is a view similar to FIGURE 3, but with the thread cutter in cutting position; and

FIGURE 5 is a sectional view taken on line 5-5 of FIGURE 4 and rotated 90 degrees.

Similar characters of reference indicate similar or identical elements and portions throughout the specification and throughout the views of the drawing.

While the thread cutter is adaptable to various sewing machines, it is particularly effective on a continuously running interrupted stitch machine such as shown and described in my US. Patent No. 3,187,700, entitled, Sewing Machine Having Automatic Interrupter. Suificient structure of this machine will be described to demonstrate the action of the thread cuter, but is to be considered merely an example.

The sewing machine 10 is basically conventional except the needle can be instantly stopped and started while the drive motor runs continuously, thus providing sharp interruption of stitching without clutch devices.

Needle 12 is carried on a vertically slidable needle bar 14, to which is fixed a thread arm 16 extending from the side of the machine. A spring 18 fitted on the needle bar between the top of the machine and the thread arm 16 biases the needle downwardly through the platform 20. A portion of spring 18 in FIGURE 2 is omited for clarity. Slidably mounted on needle bar 14 below the thread arm is a yoke 22, which is coupled by a connecting rod 24 to a rotor 26 driven by the usual rotary drive mechanism of the machine. The yoke 22 is lifted by the rotor 26 to raise needle 12 and the spring 18 drives the needle back down on each revolution of the mechanism. Thread arm 16 has a lug 28 which projects through a vertical slot 30 in a support plate 32 on the end of the machine. -Pivotally mounted on support plate 32 is a bellcrank 34 having a long arm 36 extending from the side of the machine and a short arm 38 extending upwardly, generally alongside slot 30. At the upper end of short arm 38 is a notch forming a shoulder 40, which will engage under lug 28 when the long arm 36 is raised, so locking the thread arm 16 and needle bar 14 at the top of the stitching stroke, as in broken line in FIGURE 2. As the machine continues to run the yoke 22 slides on needle bar 14 without any effect. Upon release of lug 28 from the bellcrank 34 the needle is instantly brought into operation again.

At the side of the machine is a rod 42 which passes through an eye 44 at the end of long arm 36, the eye being held between springs 46 and 48 to provide a resilient coupling to said rod. The upper end of rod 42 is connected to one end of an arm 50 pivotally mounted on the machine, the other end of said arm being coupled by a link 52 to a lever 54 at the base of the machine. An actuating rod 56 is coupled to lever 54, so that a downward pull thereon lifts rod 42 and locks the needle up, while an upward push on the actuating rod release the needle. A foot pedal, or any suitable mechanism or timing device can be used to operate actuating rod 56. The looper 58 is conventional, and swings back and forth across the needle when the needle is at the bttom of its travel to pick up the thread and make and look a stitch.

Thus far the structure described in that of the sewing machine shown in the above mentioned US. patent. The thread cutter is designed to operate simultaneously with the stitching interrupter mechanism.

The thread cutter assembly includes a cutter bar 60 pivotally attached at one end to a boss 62 below the platform 20 and being free to swing in a plane generally parallel to the platform. Attached to the cutter bar is a blade 64 of circular form and having a peripheral cutting edge, the blade being held by a central screw 66. Blade 64 is spaced below the platform 10 so that the looper 58 of the sewing machine passes just below the edge of the blade, with the blade edge very close to the needle toward the side to which the looper returns after picking up the thread. The free end of cutter bar 60 has a downwardly turned stop lug 68, the specific shape of the bar and stop lug being dependent on the space available around the stitching mechanism of the particular machine. Secured below platform is a stop bracket 70 having a protruding stop 72 against which the stop lug 68 can bear, said bracket being held by screws 74 through slotted holes 76 so that, when the stop lug engages the stop, the blade 64 is precisely positioned adjacent the needle. By means of the slotted holes 76 the bracket 70 canbe adjusted to obtain accurate positioning and can thus be set to accommodate a blade which is reduced in size by sharpening.

Cutter bar 60 is biased to the cutting position by a spring 78 between stop lug 68 and bracket 70 and is held back from the needle by a retraction rod 80 having a hook portion 82 which engages the cutter bar. Retraction rod 80 is coupled to the stitch interrupter mechanism, such as through a bellcrank 84 and link 86 to the lever 54. When the needle is being driven normally the cutter bar 60 is held in retracted position, but as soon as the mechanism is actuated to stop the needle the retraction rod 80 releases the cutter bar and spring 78 pulls the unit into cutting position, as in broken linein FIGURE 3.

The mechanical coupling of the thread cutter to the stitch interrupter is one suitable arrangement for the particular machine illustrated. It will be evident that various means can be used to operate the thread cutter in synchronization with or independently of a stitch interrupter, such as by solenoids, cams, or the like.

In operation the cutter bar 60 is held retracted and does not interfere with stitching in any way. As soon as the mechanism is operated to interrupt stitching the cutter bar is released and pulled over against stop 72 by spring 78, to put the blade 64 close to needle 12. In that particular stitching stroke the looper 58 picks up the thread 88 from needle 12 and the thread is caught by the enlarged head 90 of the looper. When the looper swings back the thread is pulled across the edge of blade 64, as indicated by the directional arrow in FIGURE 4, the slicing action cutting the thread cleanly. At the same time the pull on the thread holds the last stitch tight and prevents unravelling by leaving a tail of thread below the material.

The precise timing of the cutter action is not critical. It the cutter is released while the needle is descending the stitch will be made and the thread cut off as the needle rises, since the blade 64 does not impede progress of the needle and is stationary while cutting takes place. If the cutter is released while the needle is rising the normal return swing of the looper will cut the thread at the stitch just formed, the needle being locked in the raised position by the interrupter mechanism.

Regardless of the instant of release of the thread cutter, the cutting action takes place at the return swing of the looper 58 carrying the loop of thread 92, after the needle has been pulled back through the material being stitched, as indicated at 94 in FIGURE 5. In this conventional action of stitching the raised needle holds the thread under tension while the looper pulls the stitch tight and the stationary blade 64 takes advantage of this.

The circular blade 64 eliminates the necessity for constant replacement or sharpening. Through a small access plate 96 in the platform 20 the screw 66 can be loosened and the blade turned to bring a fresh portion of the edge into cutting position. When necessary the blade can be removed and fully sharpened by conventional means, the

adjustable bracket allowing for resetting of the blade if required to ensure proper cutting action.

It is understood that minor variation from the form of the invention disclosed herein may be made without departure from the spirit and scope of the invention, and that the specification and drawings are to be considered as merely illustrative rather than limiting.

I claim:

1. In combination with a sewing machine having a material supporting platform, a needle driven for recipro cation through said platform, a looper mounted below said platform and driven to reciprocate across the path of said needle at its lowermost position, to pick up a thread from the needle in an advance direction and to pull the thread in a loop in a return direction, the improvement of a thread cutter comprising:

a cutter bar shiftably mounted below said platform,

said cutter bar having a blade mounted thereon; means to move said cutter bar between a retracted position clear of said needle and a stationary cutting position wih the blade closely adjacent said needle, on the side of the needle at which said looper recip rocates and slightly above the path of motion of said looper whereby a thread picked up by the looper is drawn across said blade. 1

2. The combination according to claim 1, and including stop means on said platform engageable with said cutter bar in said cutting position, said stop means being adjustable to control the spacing of said cutter from said needle.

3. The combination according to claim 1, wherein said last mentioned means includes a spring biasing said cutter bar toward the cutting position, and retraction means coupled to the cutting bar to move the cutting bar in one direction against said spring.

4. The combination according to claim 1, wherein said blade is circular with a peripheral cutting edge and is rotatably adjustable to selected fixed positions on said cutting bar.

5. The combination according to claim 1 and including stitch interrupting means selectively operable to stop and,

start said needle;

and means coupling said thread cutter to said stitch interrupting means to move said cutter bar to cutting position as said needle is stopped and return said cutter bar to retracted position when said needle is started.

6. The combination according to claim 5, wherein said last mentioned means includes a spring connected to said cutter bar, biasing the cutter bar to the cutting position, and a retraction rod coupled between said cutter bar and said stitch interrupting means to retract the cutter bar against said spring.

References Cited UNITED STATES PATENTS 1,173,769 2/1916 Canman 112-252 1,395,274 11/ 1921 Hagelstein 112252 1,504,236 8/ 1924 Hagelstein 112252 1,883,654 10/1932 Ericsson 112252 3,187,700 6/ 1965 Davy 112252 X FOREIGN PATENTS 688,568 2/ 1940 Germany.

HERBERT F. ROSS, Primary Examiner. 

